ASUNCION, Paraguay, Aug. 16 -- Defense Secretary Donald H. Rumsfeld, arriving in this South American capital Tuesday, said countries in the region should help strengthen democracy in Bolivia and suggested that governments in Cuba and Venezuela have been involved in Bolivia in "unhelpful ways."

Rumsfeld's brief trip is aimed at reinforcing ties with regional democracies as they fight political instability, terrorism and drug trafficking, defense officials said. Rumsfeld will also visit Peru.

Increasing political problems in Bolivia, which borders Paraguay to the northwest, have been fostered by Cuban and Venezuelan authorities, U.S. officials contend.

U.S. officials said the challenge is to steer Bolivia toward a democratic outcome while encouraging South American neighbors to work together. Peasant groups, urban activists and socialist parties have staged repeated protests in Bolivia, a deeply impoverished country.

"Any time you see issues involving stability in a country, it is something that one wishes would be resolved in a democratic, peaceful way," Rumsfeld told reporters en route to Paraguay. "There certainly is evidence that both Cuba and Venezuela have been involved in the situation in Bolivia in unhelpful ways."

The visit was Rumsfeld's fifth to the continent since late 2002 and the first time a U.S. defense secretary has landed in Paraguay, a country about the size of California landlocked in the "tri-border" area among Brazil, Argentina and Bolivia.

The tri-border area has teemed with cocaine traffickers and smugglers, and defense officials said it might also harbor groups that finance international terrorism. One defense official who briefed reporters Tuesday said Hezbollah and Hamas, radical Islamic groups in the Middle East, "get a lot of funding" from the tri-border area. The official said further unrest in the region could leave a political "black hole" that would erode other democratic efforts.